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The water supply dam built in the 1950’s blocked upstream movement for all fish. Over time, the reservoir filled with fine sediment, forming an impounded high-value wetland. The stream flowed over the dam’s spillway, which consisted of a concrete box culvert. The spillway created a 4 ft (1.2 m) drop into a shallow plunge pool.

Michael Love & Associates served as the fish passage engineers for the project, and was tasked with preserving the upstream impounded wetland for juvenile coho rearing habitat while providing fish passage over the dam. The preferred approach involved removal of the concrete spillway and construction of a nature-like roughened rock channel through a cut in the dam. The roughened channels was designed to (1) maintain the existing upstream grade, (2) avoid release of stored sediments, and (3) provide upstream and downstream passage for all native fish and other aquatic organisms.

The roughened channel is 100 feet long, with an average slope of 5-percent. The shape and features of the roughened channel are intended to create a hydraulic environment similar to a natural channel of similar slope. Since the upstream channel material is mostly fine grain sands and silts, the larger rock in the roughened channel will not be replenished if it transported downstream. Therefore, the rock used in the roughened channel was designed to be stable up to the 100-year design flow. Because the dam crest also serves as an access road, a 40-foot long prefabricated steel bridge was placed over the roughened channel at the location of the removed spillway.